Intradermal injections are used for delivering a variety of substances. Many of these substances have proven to be more effectively absorbed into or react with the immune response system of the body when injected intradermally. Recently, clinical trials have shown that hepatitis B vaccines administered intradermally are more immunogenic than if administered intramuscularly. In addition, substances have been injected intradermally for diagnostic testing, such as, for example, using what is known in the art as the “Mantoux procedure” to determine immunity status of the animal against tuberculosis and immediate hypersensitivity status of type 1 allergic diseases.
An intradermal injection is made by delivering the substance into the dermis of a patient. Below the dermis layer is subcutaneous tissue (also sometimes referred to as the hypodermis layer) and muscle tissue, in that order. Generally, the outer skin layer, epidermis, has a thickness of between 50 to 200 microns, and the dermis, the inner and thicker layer of the skin, has a thickness between 1.5 to 3.5 millimeters. Therefore, a needle cannula that penetrates the skin deeper than about 3.0 millimeters has a potential of passing through the dermis layer of the skin and making the injection into the subcutaneous region, which may result in an insufficient immune response, especially where the substance to be delivered intradermally has not been indicated for subcutaneous injection.
The Mantoux procedure for making an intradermal injection is known to be difficult to perform, and therefore dependent upon experience and technique of the health care worker. Typically, the skin is stretched and a needle cannula is inserted into the skin at an angle varying from around 10 to 15 degrees relative to the plane of the skin. Once the cannula is inserted, fluid is injected to form a blister or wheal in the dermis in which the substance is deposited or otherwise contained. The formation of the wheal is critical to proper delivery of the substance into the intradermal layer of the skin. With the Mantoux procedure, the needle cannula may penetrate the skin at too shallow a depth to deliver the substance and result in what is commonly known in the art as “wet injection” because of reflux of the substance from the injection site.
An intradermal delivery device that enables administering an intradermal injection at a 90 degree angle to the skin of the patient is disclosed in U.S. Pat. No. 6,494,865. The intradermal delivery device disclosed in that patent provides a flat skin engaging surface (see, e.g., FIG. 1, reference character 20).